The present invention relates generally to the field of down hole near infrared spectral analysis of formation fluids and in particular to rigid redundant light source for near infrared spectral analysis having a single collimating lens.
Conventional near infrared spectral analysis tools provide a light source for supplying infrared energy for spectral analysis. The light source is usually an incandescent bulb which is aligned to focus light on a down hole fluid analysis for obtaining either absorbent or reflectance spectral data. Near infra spectral data gathering instruments and the associated light sources are well known in the art. See, for example, U.S. Pat. No. 4,994,671, by Safinya et al., entitled, Apparatus and Method for Analyzing the Composition of Formation Fluids.
There is no known prior art for rigidly mounting more than one efficient optical lamp source array in a minimum packaging configuration which will satisfactorily serve a single collimating lens with a common optical axis. One application where this need arises is in providing more than one light source for a single detector for spectral analysis.
There is a current need for down hole near infrared spectral analysis tool, which inherently involves the use of a light source. Small, efficient, low wattage, high output commercially available light sources are inherently more prone to failure than the electronic detection devices used for spectral analysis. It is therefore prudent to provide a back-up light source or sources to avoid abandoning a job when a single lamp fails and the crew is forced to return to the base to replace the light source. In the early stages of introducing a tool to the field, back-up tools may not be available on all jobs and thus will not be a reality. Moreover, a customer could be discouraged and might not be anxious to make a second trip in the bore hole for NIR data.
An alternative is to provide a redundant light source on a rotary motor that rotates the expended light source out of alignment with the down hole sample and rotates the redundant lamp into alignment. The problem with utilizing such an electric motor is that it expends power in a limited power budget provided by a down hole power supply or battery. The electric motor also adds to the complexity and weight of a down hole tool. Another alternative is to utilize a prism or special bulb developed with multiple filaments feeding a single, large lens, however, such a design is complex and a cracked bulb or lead seal might cause all the filaments to fail simultaneously. Thus there is a need for a simple redundant light source that does not deplete the down hole power supply or require rotation of the redundant light source.
The present invention provides a rigid redundant light source for obtaining down hole near infrared data. Primary and second light sources, collimating lens, sample tube and filter are provided and positioned to minimize off-axis errors caused by mounting two light sources symmetrically about the optical axis of collimating beam. A rigid redundant light source for obtaining down hole near infrared data in a NIR data acquisition instrument is provided having a plurality of lamps positioned in close proximity to each other and symmetrically about a common optical axis for a single collimating lens. A single collimating lens system for capturing and collimating the light is provided. The structure is arranged and dimensioned so that a single collimating lens can be used for a plurality of light sources with affecting the data. A switch and sensor is provided for turning on an alternate light source when a first light source burns out. A filter is rotated 90 degrees with respect to the light sources to minimized off axis error generated when switching between light sources.
A plurality of small diameter light sources are positioned close together an optimal distance from the single collimating lens to enable the use of a single lens for more than one light source.